The present invention relates to a method and apparatus for converting data, a method and apparatus for inverse converting data, a method and system for processing information, a recording medium, and a computer program. More specifically, the present invention relates to a method and apparatus for converting data, a method and apparatus for inverse converting data, a method and system for processing information, a recording medium, and a computer program for discouraging unauthorized copying using an analog video signal by substantially degrading the video data in second and subsequent encoding and decoding operations in a manner free from any inconveniences, such as an increase in circuit scale, involved.
FIG. 1 illustrates a known video display system. The video display system includes a reproducing apparatus 1 and a display 2.
The reproducing apparatus 1 includes a decoder 11 and digital-to-analog (D/A) converter 12. The decoder 11 decodes encoded digital video signal reproduced from a recording medium such as an optical disk (not shown), and supplies a digital video signal Vdg0, obtained as a result, to the D/A converter 12. The D/A converter 12 converts the digital video signal Vdg0 into an analog video signal Van, and outputs the analog video signal Van to the outside. The analog video signal Van, output from the reproducing apparatus 1, is supplied to the display 2.
The display 2, composed of a cathode-ray tube (CRT) display, a liquid-crystal display (LCD), or the like, displays an image corresponding to the analog video signal Van supplied from the reproducing apparatus 1.
As shown in FIG. 1, a known encoding apparatus 3 includes an analog-to-digital (A/D) converter 21, an encoder 22, and a recorder 23. Unauthorized copying can be performed using the analog video signal Van output from the encoding apparatus 3 and the reproducing apparatus 1.
When the analog video signal Van output from the reproducing apparatus 1 is input to the encoding apparatus 3, the A/D converter 21 analog-to-digital converts the analog video signal Van, thereby outputting the resulting digital video signal Vdg′ to the encoder 22. The encoder 22 encodes the digital video signal Vdg′, thereby outputting the resulting encoded digital video signal Vcd′ to the recorder 23. The recorder 23 records the encoded digital video signal Vcd′ onto a recording medium such as an optical disk (not shown). Unauthorized copying can thus be performed.
Japanese Unexamined Patent Application Publication No. 2001-245270 discloses one technique. In accordance with the disclosed technique, an analog video signal Van, which is copyright protected, is scrambled or prevented from being output to control unauthorized copying using the analog video signal Van.
In accordance with Japanese Unexamined Patent Application Publication No. 10-289522, a compression decoding unit in at least one of a reproducing section and a recording section includes a noise information generator. Noise information that cannot be identified by only a single video reproduction process is embedded in a digital video signal. Copying operation itself is enabled. If a copying operation is repeated by a plurality of times, an image is severely degraded, and the number of copying cycles is thus limited in practice.
In accordance with the technique disclosed in Japanese Unexamined Patent Application Publication No. 2001-245270, unauthorized copying is controlled because the analog video signal Van is scrambled or prevented from being output. On the other hand, a normal image cannot be displayed on the display 2, either.
In accordance with the technique disclosed in Japanese Unexamined Patent Application Publication No. 10-289522, the reproducing section and/or the recording section needs the noise information generator and a circuit for embedding noise information. Circuit scale is thus increased.
More specifically, although unauthorized copying using the analog video signal Van is prevented in accordance with the techniques disclosed in Japanese Unexamined Patent Application Publication Nos. 2001-245270 and 10-289522, an appropriate image cannot be displayed on the display 2 and the circuit scale is increased.
Japanese Unexamined Patent Application Publication No. 2004-289685 assigned to the same assignee of the present invention proposes a technique that controls unauthorized copying using the analog video signal in a manner free from the problems that no correct images are displayed, and that the circuit scale is increased.
In accordance with the technique proposed in Japanese Unexamined Patent Application Publication No. 2004-289685, a phase of a digital video signal that is obtained by analog-to-digital converting an analog video signal is shifted, and the phase-shifted digital video signal is encoded. Copying is made impossible without degrading the quality of an image, i.e., with the quality of the image maintained. Thus, unauthorized copying using the analog video signal is discouraged.
The technique proposed in Japanese Unexamined Patent Application Publication No. 2004-289685 makes unauthorized copying difficult. In the current environment where digital content is widely available, there is a need for a further technique for unauthorized copying prevention in addition to the technique proposed in Japanese Unexamined Patent Application Publication No. 2004-289685.